1. Field of the Invention
The invention relates generally to vehicular mounted stabilized gyroscopic instruments and specifically to a gyrocompass that provides both navigation data and stabilization data without the utilization of an accelerometer or separate gravity sensors.
2. Description of the Prior Art
Stabilized vehicular mounted gyrocompasses for providing both navigation data and stabilization data are not broadly new and have heretofore been taught, e.g., in U.S. Pat. No. 2,729,108, entitled "Control Systems for Gyroscopic Instruments", issued to Vacquier et al, issued on Jan. 3, 1956 and assigned to the Applicants' assignee. The apparatus disclosed in the Vacquier et al patent includes a pair of gyros of the directional type whose rotors normally spin about horizontal axes. The frames for the respective gyroscopic rotors are independently mounted on a common support. The frames for the rotors are interconnected by a slaving means adapted to maintain the spin axes of the rotors in mutually perpendicular relation. The instrument is provided with azimuthal directivity by gravity responsive means for the meridan gyro of the sensitive element whereby its horizontal spin axis is maintained in a north-south direction due to the effect thereon of the horizontal component of the earth's rotation. The slave gyro of the sensitive element includes a frame supporting a rotor whose horizontal spin axis points in an east-west direction. Both gyros are mounted in neutral equilibrium on a common support. The frames of both gyros are levelled with the spin axes of the rotors thereof in a horizontal plane as by means including electrolytic levels providing limited substantially linear signal outputs with tilt of the frames from a level condition. The support for the gyros includes an azimuth or phantom member with freedom about a vertical axis that is mounted on a platform having freedom relative to the mutually perpendicular pitch and roll axes of the craft. The azimuth member and platform are respectively positioned by an azimuth servomotor and pitch and roll servomotors. The platform and azimuth member are effectively stabilized by a follow-up control from the sensitive element of the gyroscopic instrument which includes the respective servomotors. Azimuth, pitch and roll data transmitters are also operated by the respective servomotors.
It is well known to those skilled in the art that in order for a gyrocompass of the type taught in the Vacquier patent to remain continuously pointing north in the presence of vehicular velocity and acceleration, compensation for these dynamic effects must normally be introduced. In the Vacquier patent this compensation is provided by a gravitationally responsive device having an electrolytic liquid which when coupled to an electronic processor means provides a signal representative of the acceleration of the vehicle in a north-south direction. Improvements in the art have resulted in accelerometers of the type taught in U.S. Pat. No. 2,840,366, entitled "Accelerometers", issued to W. G. Wing, on June 24, 1958, and assigned to the Applicants' assignee. Consequently, it is now conventional within the art to use an accelerometer which senses the northerly acceleration and which then integrates the acceleration signal to provide an inertia north velocity for precessing the meridian or north-seeking gyro about the east axis and for compassing the platform to the north. The compassing signal is ordinarily based upon a comparison between the inertial north velocity term and the northerly component of the vehicle's velocity.
The conventional stabilized gyrocompass incorporating accelerometers is relatively expensive, occupies on the order of 61/2 cubic feet, and weighs on the order of 450 pounds. To date, it has been impractical to utilize such devices on small naval patrol craft. However, with the advent of smaller more sophisticated weapons systems requiring stabilization, there is a need for a less expensive and more compact stabilized gyrocompass. Accordingly, the practice of the present invention provides a less expensive and more compact stabilized gyrocompass which provides a simplified compensation means for vehicular velocity and acceleration and which does not use an accelerometer or separate gravity sensor and thus makes it feasible to incorporate stabilized gyrocompasses in small naval patrol craft.